Azeotrope-like compositions of 1,1-dichloro-1-fluoroethane, dichlorotrifluoroethane and ethanol

ABSTRACT

Azeotrope-like compositions comprising 1,1-dichoro-1-fluoroethane, dichlorotrifluoroethane and ethanol are stable and have utility as degreasing agents and as solvents in a variety of industrial cleaning applications including cold cleaning and defluxing of printed circuit boards.

CROSS-REFERENCE TO RELATED APPLICATIONS

Co-pending, commonly assigned application Ser. No. 204,340, filed06/09/88, discloses azeotrope-like mixtures of1,1-dichloro-1-fluoroethane and ethanol.

Co-pending, commonly assigned application Ser. No. 297,467, filed01/17/89, which is a continuation-in-part of application Ser. No.290,124, filed 12/27/88, discloses azeotrope-like mixtures of1,1-dichloro-1-fluoroethane, dichlorotrifluoroethane and methanol.

DESCRIPTION Field of the Invention

This invention relates to azeotrope-like or essentially constant boilingmixtures of 1,1-dichloro-1-fluoroethane, dichlorotrifluoroethane andethanol. These mixtures are useful in a variety of vapor degreasing,cold cleaning and solvent cleaning applications including defluxing.

BACKGROUND OF THE INVENTION

Vapor degreasing and solvent cleaning with fluorocarbon based solventshave found widespread use in industry for the degreasing and otherwisecleaning of solid surfaces, especially intricate parts and difficult toremove soils.

In its simplest form, vapor degreasing or solvent cleaning consists ofexposing a room temperature object to be cleaned to the vapors of aboiling solvent. Vapors condensing on the object provide clean distilledsolvent to wash away grease or other contamination. Final evaporation ofsolvent from the object leaves behind no residue as would be the casewhere the object is simply washed in liquid solvent.

For difficult to remove soils where elevated temperature is necessary toimprove the cleaning action of the solvent, or for large volume assemblyline operations where the cleaning of metal parts and assemblies must bedone efficiently and quickly, the conventional operation of a vapordegreaser consists of immersing the part to be cleaned in a sump ofboiling solvent which removes the bulk of the soil, thereafter immersingthe part in a sump containing freshly distilled solvent near roomtemperature, and finally exposing the part to solvent vapors over theboiling sump which condense on the cleaned part. In addition, the partcan also be sprayed with distilled solvent before final rinsing.

Vapor degreasers suitable in the above-described operations are wellknown in the art. For example, Sherliker et al. in U.S. Pat. No.3,085,918 disclose such suitable vapor degreasers comprising a boilingsump, a clean sump, a water separator, and other ancillary equipment.

Cold cleaning is another application where a number of solvents areused. In most cold cleaning applications the soiled part is eitherimmersed in the fluid or wiped with rags or similar objects soaked insolvents and allowed to air dry.

Fluorocarbon solvents, such as trichlorotrifluoroethane, have attainedwidespread use in recent years as effective, nontoxic, and nonflammableagents useful in degreasing applications and other solvent cleaningapplications. Trichlorotrifluoroethane has been found to havesatisfactory solvent power for greases, oils, waxes and the like. It hastherefore found widespread use for cleaning electric motors,compressors, heavy metal parts, delicate precision metal parts, printedcircuit boards, gyroscopes, guidance systems, aerospace and missilehardware, aluminum parts and the like.

The art has looked towards azeotropic compositions including the desiredfluorocarbon components such as trichlorotrifluoroethane which includecomponents which contribute additionally desired characteristics, suchas polar functionality, increased solvency power, and stabilizers.Azeotropic compositions are desired because they do not fractionate uponboiling. This behavior is desirable because in the previously describedvapor degreasing equipment with which these solvents are employed,redistilled material is generated for final rinse-cleaning. Thus, thevapor degreasing system acts as a still. Unless the solvent compositionexhibits a constant boiling point, i.e., is an azeotrope or isazeotrope-like, fractionation will occur and undesirable solventdistribution may act to upset the cleaning and safety of processing.Preferential evaporation of the more volatile components of the solventmixtures, which would be the case if they were not an azeotrope orazeotrope-like, would result in mixtures with changed compositions whichmay have less desirable properties, such as lower solvency towardssoils, less inertness towards metal, plastic or elastomer components,and increased flammability and toxicity.

The art is continually seeking new fluorocarbon based azeotropicmixtures or azeotrope-like mixtures which offer alternatives for new andspecial applications for vapor degreasing and other cleaningapplications. Currently, of particular interest, are such azeotrope-likemixtures which are based on fluorocarbons which are considered to bestratospherically safe substitutes for presently used fully halogenatedchlorofluorocarbons. The latter are suspected of causing environmentalproblems in connection with the earth's protective ozone layer.Mathematical models have substantiated that hydrochlorofluorocarbons,such as 1,1-dichloro-1-fluoroethane (HCFC-141b) anddichlorotrifluoroethane (HCFC-123 or HCFC-123a), will not adverselyaffect atmospheric chemistry, being negligible contributors to ozonedepletion and to green-house global warming in comparison to the fullyhalogenated species.

U.S. Pat. No. 3,936,387 discloses the azeotropic composition of methanolwith 1,2-dichloro-1-fluoroethane (HCFC-141) U.S. Pat. No. 4,035,258discloses the azeotropic composition of ethanol with HCFC-141.

It is an object of this invention to provide novel azeotrope-likecompositions based on HCFC-141b and dichlorotrifluoroethane which areliquid at room temperature and which will not fractionate under theprocess of distillation or evaporation, which are useful as solvents foruse in vapor degreasing and other solvent cleaning applicationsincluding defluxing applications.

Another object of the invention is to provide novel environmentallyacceptable solvents for use in the aforementioned applications.

Other objects and advantages of the invention will become apparent fromthe following description.

DESCRIPTION OF THE INVENTION

In accordance with the invention, novel azeotrope-like compositions havebeen discovered comprising HCFC-141b, dichlorotrifluoroethane andethanol. The dichlorotrifluoroethane component can be either of itsisomers 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) or1,2-dichloro-1,2,2-trifluoroethane (HCFC-123a), or mixtures thereof. Thepreferred isomer is HCFC-123.

Dichlorotrifluoroethane and HCFC-141b do not form binary azeotropesystems. HCFC-141, dichlorotrifluoroethane and methanol do not form aternary azeotropic system. HCFC-141, dichlorotrifluoroethane and ethanolare not known to form a ternary azeotropic system.

The azeotrope-like compositions of the invention comprise from about62.5 to about 94.9 weight percent of HCFC-141b, from about 3.0 to about35.5 weight percent of dichlorotrifluoroethane and from about 0.1 toabout 3.0 weight percent of ethanol.

In a preferred embodiment of the invention, the azeotrope-likecompositions of the invention comprise from about 72 to about 94.7weight percent of HCFC-141b, from about 5 to about 26.0 weight percentof dichlorotrifluoroethane and from about 0.3 to about 2.0 weightpercent of ethanol.

In a still more preferred embodiment of the invention, theazeotrope-like compositions of the invention comprise from about 75 toabout 90 weight percent of HCFC-141b, from about 8.0 to about 24.7weight percent of dichlorotrifluoroethane and from about 0.3 to about1.5 weight percent of ethanol.

In the most preferred embodiment of the invention, the azeotrope-likecompositions of the invention comprise from about 77.2 to about 90.3weight percent HCFC-141b, about 8.1 to about 21.7 weight percentdichlorotrifluoroethane and about 0.5 to about 2.0 weight percentethanol which exhibits a boiling point of about 31.8° C. at 760 mm Hg.

The azeotrope-like compositions of the invention containing a mixture ofHCFC-123 and HCFC-123a behave as an azeotrope-like composition becausethe separate ternary azeotropic compositions with HCFC-123 and HCFC-123ahave boiling points so close to one another as to be indistinguishablefor practical purposes.

The precise or true azeotrope compositions have not been determined buthave been ascertained to be within the indicated ranges. Regardless ofwhere the true azeotropes lie, all compositions within the indicatedranges, as well as certain compositions outside the indicated ranges,are azeotrope-like, as defined more particularly below.

It has been found that these azeotrope-like compositions are on thewhole nonflammable liquids, i.e. exhibit no flash point when tested bythe Tag Open Cup test method--ASTM D 1310-86.

From fundamental principles, the thermodynamic state of a fluid isdefined by four variables: pressure, temperature, liquid composition andvapor composition, or P-T-X-Y, respectively. An azeotrope is a uniquecharacteristic of a system of two or more components where X and Y areequal at the stated P and T. In practice, this means that the componentsof a mixture cannot be separated during distillation, and therefore areuseful in vapor phase solvent cleaning as described above.

For the purpose of this discussion, by azeotrope-like composition isintended to mean that the composition behaves like a true azeotrope interms of its constant boiling characteristics or tendency not tofractionate upon boiling or evaporation. Such composition may or may notbe a true azeotrope. Thus, in such compositions, the composition of thevapor formed during boiling or evaporation is identical or substantiallyidentical to the original liquid composition. Hence, during boiling orevaporation, the liquid composition, if it changes at all, changes onlyto a minimal or negligible extent. This is to be contrasted withnon-azeotrope-like compositions in which during boiling or evaporation,the liquid composition changes to a substantial degree.

Thus, one way to determine whether a candidate mixture is"azeotrope-like" within the meaning of this invention, is to distill asample thereof under conditions (i.e. resolution-number of plates) whichwould be expected to separate the mixture into its separate components.If the mixture is non-azeotropic or non-azeotrope-like, the mixture willfractionate, i.e. separate into its various components with the lowestboiling component distilling off first, and so on. If the mixture isazeotrope-like, some finite amount of a first distillation cut will beobtained which contains all of the mixture components and which isconstant boiling or behaves as a single substance. This phenomenoncannot occur if the mixture is not azeotrope-like i.e., it is not partof an azeotropic system. If the degree of fractionation of the candidatemixture is unduly great, then a composition closer to the true azeotropemust be selected to minimize fractionation. Of course, upon distillationof an azeotrope-like composition such as in a vapor degreaser, the trueazeotrope will form and tend to concentrate.

It follows from the above that another characteristic of azeotrope-likecompositions is that there is a range of compositions containing thesame components in varying proportions which are azeotrope-like. Allsuch compositions are intended to be covered by the term azeotrope-likeas used herein. As an example, it is well known that at differingpressures, the composition of a given azeotrope will vary at leastslightly as does the boiling point of the composition. Thus, anazeotrope of A and B represents a unique type of relationship but with avariable composition depending on temperature and/or pressure.Accordingly, another way of defining azeotrope-like within the meaningof this invention is to state that such mixtures boil within about ±0.5°C. (at about 760 mm Hg) of the boiling point of the most preferredcompositions disclosed herein, i.e. 31.8° C. at 760 mm Hg. When thedichlorotrifluoroethane component is 1,1-dichloro-1,2,2-trifluoroethane,the preferred mixtures boil within about ±0.5° C. (at about 760 mm Hg)of 32.0° C. When the dichlorotrifluoroethane component is1,1-dichloro-2,2,2-trifluoroethane, the preferred mixtures boil withinabout ±0.5° C. (at about 760 mm Hg) of 31.6° C. As is readily understoodby persons skilled in the art, the boiling point of the azeotrope willvary with the pressure.

In the process embodiment of the invention, the azeotrope-likecompositions of the invention may be used to clean solid surfaces bytreating said surfaces with said compositions in any manner well knownto the art such as by dipping or spraying or use of conventionaldegreasing apparatus.

The HCFC-141b, dichlorotrifluoroethane and ethanol components of thenovel solvent azeotrope-like compositions of the invention are knownmaterials. Preferably they should be used in sufficiently high purity soas to avoid the introduction of adverse influences upon the solvencyproperties or constant boiling properties of the system.

Of the possible binary combinations of the three components which formthe azeotrope-like mixtures of this invention, only one is known to forman azeotrope: HCFC-141b and ethanol (31.9° C. boiling point at 765 mmHg), a minimum boiling azeotrope. Neither HCFC-141b and HCFC-123 norHCFC-123 and ethanol form binary azeotropes.

The advantages of the ternary systems over the binary azeotrope,HCFC-141b/ethanol, are: (a) decreased vapor flammability in comparisonto HCFC-141b/ethanol, and (b) lower ozone depletion potential comparedto HCFC-141b/ethanol.

EXAMPLES 1-4

These examples confirm the existence of azeotrope-like mixtures between1,1-dichloro-1-fluoroethane, ethanol and dichlorotrifluoroethane via themethod of distillation. These examples also illustrate that thesemixtures do not fractionate during distillation.

A 5-plate Oldershaw distillation column with a cold water condensedautomatic liquid dividing head was used for these examples. Thedistillation column was charged with the below indicated startingmixture which was heated under total reflux for about an hour to ensureequilibration. A reflux ratio of 2:1 was employed for the distillation.Approximately 50 percent of the original charges were collected in foursimilar-sized overhead fractions. The compositions of these fractionswere analyzed using gas chromatrography. Table I shows the compositionsof the starting material, the distillate fractions and the boilingpoints of the constant boiling fractions. The averages of the distillatefractions and the overhead temperatures are quite constant within theuncertainty associated with determining the compositions, indicatingthat the mixtures are constant boiling or azeotrope-like.

                  TABLE 1                                                         ______________________________________                                        Starting Material (WT. %)                                                     Example                                                                              HCFC-141b   HCFC-123  HCFC-123a ETOH                                   ______________________________________                                        1      88.90       10.07     --        1.03                                   2      74.18       24.80     --        1.02                                   3      89.11       --        9.89      1.00                                   4      74.26       --        24.72     1.02                                   ______________________________________                                        Distillate Fractions (WT. %)                                                  Example                                                                              HCFC-141b   HCFC-123  HCFC-123a ETOH                                   ______________________________________                                        1      87.5        11.12     --        1.38                                   2      71.05       27.95     --        1.00                                   3      88.55       --        10.22     1.23                                   4      73.26       --        25.72     1.02                                   ______________________________________                                                                       Boiling Point (° C.)                           Boiling    Barometric   Corrected to                                   Example                                                                              Point (°C.)                                                                       Pressure (mm Hg)                                                                           760 mm Hg                                      ______________________________________                                        1      30.5       740          31.3                                           2      31.0       740          31.8                                                             mean         31.6                                           3      31.1       748          31.7                                           4      31.8       748          32.3                                                             mean         32.0                                           ______________________________________                                    

The compositions of the invention are useful as solvents in a variety ofvapor degreasing, cold cleaning and solvent cleaning applicationsincluding defluxing.

It is known in the art that the use of more active solvents, such aslower alkanols in combination with certain halocarbons such astrichlorotrifluoroethane, may have the undesirable result of attackingreactive metals such as zinc and aluminum, as well as certain aluminumalloys and chromate coatings such as are commonly employed in circuitboard assemblies. The art has recognized that certain stabilizers, suchas nitromethane, are effective in preventing metal attack bychlorofluorocarbon mixtures with such alkanols. Other candidatestabilizers for this purpose, such as disclosed in the literature, aresecondary and tertiary amines, olefins and cycloolefins, alkyleneoxides, sulfoxides, sulfones, nitrites and nitriles, and acetylenicalcohols or ethers. It is contemplated that such stabilizers as well asother additives may be combined with the azeotrope-like compositions ofthis invention.

What is claimed is:
 1. Azeotrope-like compositions consistingessentially of from about 62.5 to about 94.9 weight percent1,1-dichloro-1-fluoroethane, from about 3.0 to about 35.5 weight percentdichlorotrifluoroethane selected from the group consisting of1,2-dichloro-1,2,2-trifluoroethane, 1,1-dichloro-2,2,2,-trifluoroethaneor mixtures thereof and from about 0.1 to about 3.0 weight percentethanol wherein the composition with 1,2,-dichloro-1,2,2-trifluoroethaneboils at about 32.0° C.±0.5° C. at 760 mm Hg, the composition with1,1-dichloro-2,2,2-trifluoroethane boils at about 31.6° C.±0.5° C. at760 mm Hg and the composition with mixtures of thedichlorotrifluoroethanes boils at about 31.8° C.±0.5° C. at 760 mm Hg.2. Azeotrope-like compositions according to claim 1 wherein saiddichlorotrifluoroethane is 1,2-dichloro-1,2,2-trifluoroethane. 3.Azeotrope-like compositions according to claim 1 wherein saiddichlorotrifluoroethane is 1,1-dichloro-2,2,2-trifluoroethane. 4.Azeotrope-like compositions according to claim 1 consisting essentiallyof from about 72.0 to about 94.7 weight percent1,1-dichloro-1-fluoroethane, from about 5.0 to about 26.0 weight percentdichlorotrifluoroethane and from about 0.3 to about 2.0 weight percentethanol.
 5. Azeotrope-like compositions according to claim 1 consistingessentially of from about 75.0 to about 90.0 weight percent1,1-dichloro-1-fluoroethane, from about 8.0 to about 24.7 weight percentdichlorotrifluoroethane and from about 0.3 to about 1.5 weight percentethanol.
 6. Azeotrope-like compositions according to claim 1 consistingessentially of about 77.2 to about 90.3 weight percent1,1-dichloro-1-fluoroethane, about 8.1 to about 21.7 weight percentdichlorotrifluoroethane and about 0.5 to about 1.5 weight percentethanol.
 7. Azeotrope-like compositions according to claim 6 whereinsaid dichlorotrifluoroethane is 1,2-dichloro-1,2,2-trifluoroethane. 8.Azeotrope-like compositions according to claim 6 wherein saiddichlorotrifluoroethane is 1,1-dichloro-2,2,2-trifluoroethane. 9.Azeotrope-like compositions consisting essentially of1,1-dichloro-1-fluoroethane, dichlorotrifluoroethane selected from thegroup consisting of 1,2-dichloro-1,2,2-trifluoroethane,1,1-dichloro-2,2,2,-trifluoroethane or mixtures thereof and ethanolwherein the composition with 1,2-dichloro-1,2,2-trifluoroethane boils atabout 32.0° C.±0.5° C. at 760 mm Hg, the composition with1,1-dichloro-2,2,2-trifluoroethane boils at about 31.6° C.±0.5° C. at760 mm Hg and the composition with mixtures of thedichlorotrifluoroethanes boils at about 31.8° C.±0.5° C. at 760 mm Hg.10. Azeotrope-like compositions according to claim 9 wherein saiddichlorotrifluoroethane is 1,2-dichloro-1,2,2-trifluoroethane which boilat about 32.0° C.±0.5° C. at 760 mm Hg.
 11. Azeotrope-like compositionsaccording to claim 9 wherein said dichlorotrifluoroethane is1,1-dichloro-2,2,2-trifluoroethane which boil at about 31.6° C.±0.5° C.at 760 mm Hg.
 12. The method of cleaning a solid surface which comprisestreating said surface with an azeotrope-like composition as defined inclaim
 1. 13. The method of cleaning a solid surface which comprisestreating said surface with an azeotrope-like composition as defined inclaim
 2. 14. The method of cleaning a solid surface which comprisestreating said surface with an azeotrope-like composition as defined inclaim
 3. 15. The method of cleaning a solid surface which comprisestreating said surface with an azeotrope-like composition as defined inclaim
 4. 16. The method of cleaning a solid surface which comprisestreating said surface with an azeotrope-like composition as defined inclaim
 9. 17. The method of cleaning a solid surface which comprisestreating said surface with an azeotrope-like composition as defined inclaim
 10. 18. The method of cleaning a solid surface which comprisestreating said surface with an azeotrope-like composition as defined inclaim 11.